Proton-Catalyzed Interconversion of Tungsten(VI) Imido Isopropylidene and Propylene Complexes

Additions of two equivalents of (CF₃)₃COH (R_F9OH) or (CF₃)₂MeCOH (R_F6OH) to W(NAr)₂R₂ complexes (Ar = 2,6-diisopropylphenyl, R = n-propyl or i-propyl) offer the opportunity to synthesize propylene or isopropylidene olefin metathesis-active complexes in the absence of free propylene. Propylene and isopropylidene complexes (W(NAr)(ArNH₂)(OR_F9)₂(propylene) and W(NAr)(ArNH₂)(OR_F9)₂(CMe₂)) are formed at room temperature from both W(NAr)₂(i-propyl)₂ and W(NAr)₂(n-propyl)₂ complexes upon addition of two equivalents of R_F9OH; no W = CHCH₂Me complexes are observed. Similar results are found for W(NAd)₂(propyl)₂ complexes (Ad = 1-adamantyl). Both RNH₂ and RNH₂B(C₆F₅)₃ (R = Ar or Ad) catalyze the interconversion of propylene and isopropylidene complexes. Addition of R_F6OH to W(NAr)₂R₂ or W(NAd)₂R₂ complexes leads to mixtures that contain largely propylene complexes. Addition of (CF₃)Me₂COH (R_F3OH) to W(NAr)₂(i-Pr)₂ yields only propylene complexes. One propylene complex, W(NAd)(OR_F9)₂(CH₂═CHMe)(dme), was isolated, structurally characterized, and found to react with AdNH₂ to reform W(NAd)(OR_F9)₂(CMe₂)(AdNH₂). It is proposed that propylene and isopropylidene complexes interconvert through the formation of an intermediate isopropyl complex.